From: Josef 'Jeff' Sipek <jeff.sipek@dovecot.fi>
Date: Tue, 13 Sep 2016 19:01:56 +0000 (-0400)
Subject: lib: introduce container_of
X-Git-Tag: 2.3.0.rc1~1097
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=1c238d4b71b43ba80cf4b9b3c3e797f2b25ec23c;p=thirdparty%2Fdovecot%2Fcore.git

lib: introduce container_of

This is a simple but type safe implementation.
---

diff --git a/src/lib/macros.h b/src/lib/macros.h
index dc4d66db96..4cbab19320 100644
--- a/src/lib/macros.h
+++ b/src/lib/macros.h
@@ -26,6 +26,10 @@
 #define CONST_PTR_OFFSET(ptr, offset) \
 	((const void *) (((const unsigned char *) (ptr)) + (offset)))
 
+#define container_of(ptr, type, name) \
+	(type *)((uintptr_t)(ptr) - (uintptr_t)offsetof(type, name) + \
+		 COMPILE_ERROR_IF_TYPES_NOT_COMPATIBLE(ptr, &((type *) 0)->name))
+
 /* Don't use simply MIN/MAX, as they're often defined elsewhere in include
    files that are included after this file generating tons of warnings. */
 #define I_MIN(a, b)  (((a) < (b)) ? (a) : (b))